Flail Chest

Etiology

As a traumatic disorder, flail chest shares risk factors with other forms of major trauma. Male sex and intoxication are independent risk factors. Motor vehicle collisions account for approximately 75% of major trauma cases leading to flail chest, while falls, particularly among older adults, cause an additional 15%.[1] Certain high-impact injuries, such as direct blows to the thorax, are more likely to produce 2 fractures on a single rib, increasing the likelihood of a flail segment. In contrast, rollover and crush injuries tend to cause single-point rib fractures and are, therefore, less likely to result in flail chest.

Metabolic bone disorders, such as osteogenesis imperfecta, increase susceptibility in pediatric populations. Among older adults, age-related stiffening of the chest wall and underlying osteoporosis contribute to increased risk. Chronic pulmonary conditions, which are prevalent in this group, also heighten vulnerability to complications associated with flail chest.

Epidemiology

According to the American Association for the Surgery of Trauma, approximately 1% of the United States population sustains a significant traumatic injury each year. Chest trauma occurs in 20% of these cases and accounts for 25% of trauma-related deaths. Flail chest is identified in roughly 7% of patients with chest trauma.[2] Hospitalization is typically required, and flail chest occurs in isolation in fewer than 40% of cases. More commonly, this traumatic condition is accompanied by pulmonary contusions, hemothorax or pneumothorax, head injury, and occasionally major vascular injury. Reported mortality ranges from 10% to 20%, often attributable to associated injuries rather than flail chest itself.[3] Morbidity is substantial due to prolonged hospitalization and complex recovery.

Pathophysiology

Airflow into and out of the lungs depends on changes in intrathoracic pressure. Inspiration requires coordinated activation of respiratory muscle groups, including the diaphragm, external intercostals, parasternal muscles, internal intercostals, and accessory muscles. Descent of the diaphragmatic dome increases the vertical dimension of the thoracic cavity and generates negative pressure. At rest, the diaphragm alone can sustain adequate ventilation. During exercise or in pathological states, the intercostal muscles play a significant role in generating inspiratory effort. Exhalation is typically passive due to the elastic recoil of the lungs, although the abdominal and intercostal muscles may assist.

In flail chest, disruption of chest wall continuity impairs the normal biomechanical function of the ribs. The flail segment moves in paradoxical opposition to the remainder of the thoracic cage, collapsing inward during inspiration as the intact chest wall expands outward. The severity of this paradoxical motion and its physiological impact is determined by 3 factors: pleural pressure, the extent of the flail segment, and intercostal muscle activation during inspiration.[4]

A flail segment disrupts normal respiratory mechanics in 3 principal ways: ineffective ventilation, pulmonary contusion, and hypoventilation with atelectasis. Ventilation becomes ineffective due to increased dead space, reduced intrathoracic pressure, and elevated oxygen demand from injured tissues. Pulmonary contusion in the lung adjacent to the flail segment is nearly universal and results in edema, hemorrhage, and, in some cases, tissue necrosis. These changes impair gas exchange and reduce pulmonary compliance.

Hypoventilation and atelectasis arise from pain associated with the injury. Pain induces both voluntary and involuntary splinting, in which patients limit chest wall movement to avoid discomfort. This restriction leads to shallow respiration, reduced tidal volume, and an ineffective cough, all of which contribute to atelectasis, impaired gas exchange in the affected lung region, and retention of pulmonary secretions.[5]

History and Physical

The history is often evident, as flail chest typically occurs in the context of major blunt force trauma. Older adults are at increased risk. Diagnosis may be more challenging in nonverbal patients, victims of abuse, or cases without a reliable history.

The physical examination should be performed according to a systematic trauma assessment in all patients with suspected thoracic injury. The patient should be fully exposed. A complete set of vital signs should be obtained, including an accurate respiratory rate and oxygen saturation. The primary survey, comprising airway, breathing, circulation, disability, and exposure (eg, ABCDE), should be initiated, followed by the secondary survey. Bilateral breath sounds should be auscultated, and the chest should be palpated for tenderness, deformity, or crepitus. The thorax should be inspected for bruising, open wounds, or seatbelt marks. Patients typically report severe chest wall pain and may present with tachypnea, splinting, or signs of respiratory insufficiency.

Flail chest is characterized by localized pain, pronounced tenderness over the fracture site, and respiratory distress, including tachypnea and dyspnea. Paradoxical chest wall motion, when visible, is a key diagnostic sign. During inspiration, the flail segment moves inward as the rest of the chest expands. During expiration, the segment moves outward as the chest contracts. However, this pathognomonic finding may be absent, especially in patients with significant splinting and shallow respirations. Paradoxical motion may become more evident as intercostal muscle fatigue progresses. Positive pressure ventilation alters thoracic pressure dynamics and eliminates paradoxical movement. Consequently, patients on bilevel positive airway pressure or mechanical ventilation do not exhibit this sign, and the diagnosis of flail chest may only become apparent following extubation.

Evaluation

Evaluation of a patient with trauma should include all standard examinations and studies used in the assessment of individuals with major multisystem trauma. The extended focused assessment with sonography in trauma may detect pneumothorax or hemothorax, but does not typically aid in the identification of flail chest. Chest radiography is often the first imaging study that raises suspicion for flail chest. However, even with 2 views, the sensitivity of this modality is limited, and rib fractures may be missed. A rib series, which includes posteroanterior and oblique views, is more sensitive than standard chest radiographs but may still fail to detect up to one-fourth of rib fractures.[6] Relying solely on chest radiography may result in missed diagnoses.

Computed tomography (CT) is the imaging test of choice for evaluating flail chest and associated injuries. CT with 3-dimensional reconstruction provides more detailed visualization of fracture patterns and aids in clinical correlation. The finding of 3 ribs fractured in 2 locations is suggestive of a flail segment, but must be assessed in the context of clinical signs. CT imaging may also guide therapeutic decisions. Trauma laboratory testing should include arterial blood gas analysis. While laboratory studies do not directly diagnose flail chest, they are essential for monitoring the progression of evolving respiratory failure.

Treatment / Management

Nonoperative management of flail chest is guided by 5 key principles: pain control, respiratory support, pulmonary hygiene, fluid balance, and the avoidance of outdated interventions. These principles aim to restore respiratory function, reduce the need for surgical intervention, and minimize complications. Effective analgesia, particularly with regional techniques such as thoracic epidural or paravertebral blocks, is essential not only for patient comfort but also for preventing respiratory compromise. Multimodal regimens decrease opioid requirements and improve pulmonary outcomes.

Respiratory support encompasses supplemental oxygen, noninvasive ventilation (NIV), and, when necessary, invasive mechanical ventilation, using lung-protective strategies. NIV may prevent the need for intubation in selected patients, but it must be closely monitored due to the risk of failure. Pulmonary hygiene relies on deep breathing exercises, physiotherapy, and early mobilization to optimize secretion clearance and reduce the risk of atelectasis and pneumonia. Preserving mucociliary function and preventing secretion retention are essential for avoiding pulmonary complications.

Fluid management requires judicious resuscitation. Isotonic fluids may be used initially, but excessive hydration can worsen pulmonary contusion and contribute to acute respiratory distress syndrome. Obsolete interventions, such as external taping or corticosteroid administration, are no longer recommended. Prehospital care emphasizes stabilization of airway, breathing, and circulation while avoiding high-pressure ventilation that could aggravate pneumothorax. Early, coordinated interprofessional care is crucial for maintaining physiological stability, preventing complications, and minimizing the need for surgical intervention.[7](B2)

Mechanical ventilation using positive pressure, originally termed “internal pneumatic stabilization” by Avery et al in 1956, is a primary intervention for patients with flail chest complicated by respiratory failure or concomitant head or abdominal trauma requiring ventilatory support. This approach restores synchronous movement between the flail segment and the intact chest wall, thereby improving respiratory mechanics. Advancements, such as volume-limited ventilation, have contributed to a decrease in mortality in severe cases. However, prolonged mechanical ventilation poses a significant risk for ventilator-associated pneumonia, highlighting the importance of careful patient selection, close monitoring, and timely weaning.[8][9](A1)

Surgical stabilization of rib fractures (SSRF) is currently recognized as a key treatment option for patients with severe thoracic injury, particularly those with flail chest. Possible approaches include open reduction and internal fixation, minimally invasive methods such as video-assisted thoracoscopic surgery, and percutaneous procedures. These modalities aim to restore chest wall stability, alleviate pain, and improve respiratory function.

Indications and Contraindications for Surgical Stabilization of Rib Fractures

The decision to perform SSRF is guided by an assessment of the patient's clinical condition, fracture pattern, associated injuries, and facility capabilities. The 2024 position paper by the World Society of Emergency Surgery and Chest Wall Injury Society identifies key indications for SSRF. These indications include flail chest with respiratory compromise or prolonged ventilator dependence, particularly when extubation fails after 7 to 14 days, and significant chest wall deformity or volume loss exceeding 30% on imaging.

Other indications include intractable pain unresponsive to optimal nonoperative measures, symptomatic nonunion or malunion resulting in chronic pain or disability, and the opportunity to stabilize fractures during thoracotomy performed for other intrathoracic procedures. SSRF is also recommended in cases of multiple (≥3) ipsilateral displaced rib fractures associated with respiratory dysfunction, even in the absence of a flail segment, as well as in settings where pulmonary herniation is due to chest wall defects.[10]

Absolute contraindications include hemodynamic instability, rib fractures outside ribs 3 to 10 (with limited exceptions), acute myocardial infarction, and, traditionally, severe traumatic brain injury (TBI). However, emerging evidence supports the use of SSRF in select cases of TBI. Relative contraindications include being younger than 18, having substantial comorbidities, mild to moderate TBI or spinal cord injury, pleural empyema, prior chest wall irradiation, extensive soft tissue loss, and inability to position the patient safely for surgery.

Timing of Surgical Stabilization of Rib Fractures

Early surgery (within 48–72 hours) is associated with better outcomes, including a shorter duration of mechanical ventilation, a limited intensive care unit and hospital length of stay, a lower incidence of pneumonia, and a decreased need for tracheostomy. Delayed surgery (>72 hours) is less advantageous and technically more difficult, though it may still be appropriate for addressing chronic complications such as nonunion. Operating during the peak of inflammation (>72 hours) may lead to poorer outcomes.[11][12][13][14][15](A1)

Surgical Technique and Hardware

Surgical planning is guided by detailed imaging, ideally using 3-dimensional CT reconstructions. SSRF is performed under general anesthesia, often with single-lung ventilation. Incisions are designed to spare muscle tissue, and intraoperative ultrasound may assist in accurately localizing target fractures. Not all fractures require fixation. Sufficient stability is often achieved by addressing only the most displaced ribs.

Fixation equipment options include the following:

• Bicortical screw plating systems, typically precontoured titanium plates with locking screw options (eg, MatrixRib, RibFix Blu)
• U-plate systems (eg, RibLoc U Plus), which offer stronger constructs and wider load distribution
• Intramedullary devices (eg, splints, K-wires) for fractures not amenable to plating
• Bioresorbable implants, now less frequently used due to high early failure rates
• Judet struts, largely obsolete today [16]

Outcomes improve when fixation is limited to fractures contributing most to instability. This approach facilitates faster recovery and fewer complications.

Postoperative Care

Surgical wounds are closed in layers, and a chest tube is placed when the pleural cavity is entered. Perioperative analgesia may be provided using thoracic epidural catheters.

Differential Diagnosis

The following conditions should be considered in the differential diagnosis of flail chest:

• Acute aortic dissection
• Amebiasis
• Pediatric trauma considerations, such as pulmonary contusion without rib fracture, nonaccidental trauma, and congenital chest wall anomalies
• Domestic violence
• Suspected abuse in older adults
• Esophagitis
• Clavicle fracture
• Mechanical back pain
• Pneumothorax
• Pulmonary embolism
• Sternal fracture
• Upper genitourinary trauma

These conditions reflect a broad spectrum of thoracic and systemic conditions that can complicate the clinical picture in suspected flail chest cases. Accurate differentiation prevents delays in diagnosis and optimizes patient outcomes.

Prognosis

Patients who do not require mechanical ventilation generally have a better prognosis than those who do. However, adverse events are common and often result in prolonged disability, with pain persisting for months or even years in some cases.

Complications

Flail chest can lead to the following complications:

• Severe chronic pain
• Chest wall deformity
• Dyspnea
• Loss of exercise endurance

The complications of flail chest extend beyond the acute phase and can cause lasting morbidity. Early recognition and comprehensive care are essential to optimize recovery.